s.
We must, therefore, get rid of this complicated machinery, which
confuses the problem, and see if we can find the fundamental units which
show these properties, unencumbered by the secondary machinery which has
hitherto attracted our attention. We must turn now to the problem
connected with protoplasm and the living cell, since here, if anywhere,
can we find the life substance reduced to its lowest terms.

CHAPTER II.

THE CELL AND PROTOPLASM.

==Vital Properties.==--We have seen that the general activities of the
body are intelligible according to chemical and mechanical laws,
provided we can assume as their foundation the simple vital properties
of living phenomena. We must now approach closer to the centre of the
problem, and ask whether we can trace these fundamental properties to
their source and find an explanation of them.

In the first place, what are these properties? The vital powers are
varied, and lie at the basis of every form of living activity. When we
free them from complications, however, they may all be reduced to four.
These are: (1) _Irritability_, or the property possessed by living
matter of reacting when stimulated. (2) _Movement_, or the power of
contracting when stimulated. (3) _Metabolism_, or the power of absorbing
extraneous food and producing in it certain chemical changes, which
either convert it into more living tissue or break it to pieces to
liberate the inclosed energy. (4) _Reproduction_, or the power of
producing new individuals. From these four simple vital activities all
other vital actions follow; and if we can find an explanation of these,
we have explained the living machine. If we grant that certain parts of
the body can assimilate food and multiply, having the power of
contraction when irritated, we can readily explain the other functions
of the living machine by the application of these properties to the
complicated machinery of the body. But these properties are fundamental,
and unless we can grasp them we have failed to reach the centre of the
problem.

As we pass from the more to the less complicated animals we find a
gradual simplification of the machinery until the machinery apparently
disappears. With this simplification of the machinery we find the
animals provided with less varied powers and with less delicate
adaptations to conditions. But withal we find the fundamental powers of
the living organisms the same. For the performance of these fundamental